1. Field of the Invention
Embodiments of the present invention relate generally to a method and an apparatus for a drilling operation. More particularly, the invention relates to a rotating control head. Still more particularly, the invention relates to the actuation and cooling of a rotating control head.
2. Description of the Related Art
Drilling a wellbore for hydrocarbons requires significant expenditures of manpower and equipment. Thus, constant advances are being sought to reduce any downtime of equipment and expedite any repairs that become necessary. Rotating equipment is particularly prone to maintenance as the drilling environment produces abrasive cuttings detrimental to the longevity of rotating seals, bearings, and packing elements.
In a typical drilling operation, a drill bit is attached to a drill pipe. Thereafter, a drive unit rotates the drill pipe through a drive member, referred to as a kelly as the drill pipe and drill bit are urged downward to form the wellbore. In some arrangements, a kelly is not used, thereby allowing the drive unit to attach directly to the drill pipe. The length of the wellbore is determined by the location of the hydrocarbon formations. In many instances, the formations produce gas or fluid pressure that may be a hazard to the drilling crew and equipment unless properly controlled.
Several components are used to control the gas or fluid pressure. Typically, one or more blow out preventers (BOP) are mounted to the well forming a BOP stack to seal the mouth of the well. Additionally, an annular BOP is used to selectively seal the lower portions of the well from a tubular body that allows the discharge of mud through the outflow line. In many instances, a conventional rotating control head, also referred to as a rotating blow out preventor, is mounted above the BOP stack. An internal portion of the conventional rotating control head is designed to seal and rotate with the drill pipe. The internal portion typically includes an internal sealing element mounted on a plurality of bearings.
The internal sealing element may consist of both a passive seal arrangement and an active seal arrangement. The active seal arrangement is hydraulically activated. Generally, a hydraulic circuit provides hydraulic fluid to the active seal rotating control head. The hydraulic circuit typically includes a reservoir containing a supply of hydraulic fluid and a pump to communicate the hydraulic fluid from the reservoir to the rotating control head. As the hydraulic fluid enters the rotating control head, a pressure is created to energize the active seal arrangement. Preferably, the pressure in the active seal arrangement is maintained at a greater pressure than the wellbore pressure. Typically, the hydraulic circuit receives input from the wellbore and supplies hydraulic fluid to the active seal arrangement to maintain the pressure differential. However, the hydraulic circuit in the conventional active seal rotating control head has a less than desirable response time to rapidly changing wellbore pressure.
During the drilling operation, the drill pipe is axially and slidably forced through the rotating control head. The axial movement of the drill pipe causes wear and tear on the bearing and seal assembly and subsequently requires repair. Typically, the drill pipe or a portion thereof is pulled from the well and a crew goes below the drilling platform to manually release the bearing and seal assembly in the rotating control head. Thereafter, an air tugger in combination with a tool joint on the drill string are typically used to lift the bearing and seal assembly from the rotating control head. The bearing and seal assembly is replaced or reworked and thereafter the crew goes below the drilling platform to reattach the bearing and seal assembly into the rotating control head and operation is resumed. The process is time consuming and can be dangerous.
Additionally, the thrust generated by the wellbore fluid pressure and the radial forces on the bearing assembly causes a substantial amount of heat to build in the conventional rotating control head. The heat causes the seals and bearings to wear and subsequently require repair. The conventional rotating control head typically includes a cooling system that circulates oil through the seals and bearings to remove the heat. However, the oil based cooling system may be very expensive to implement and maintain.
There is a need therefore, for a cost-effective cooling system for a rotating control head. There is a further need therefore for a cooling system in a rotating control head that can be easily implemented and maintained. There is a further need for an effective hydraulic circuit to actuate the active sealing arrangement in a rotating control head and to maintain the proper pressure differential between the fluid pressure in the rotating control head and the wellbore pressure. There is yet a further need for an improved rotating control head.